Selective isomerization employing metal arsenide catalyst

ABSTRACT

A METHOD AND CATALYSTS FOR SELECTIVE HYDROGENATION AND ISOMERIZATION WHICH INVOLVES CONTACTING A FEEDSTREAM WITH HYDROGEN AND WITH VARIOUS SUPPORTED CATALYSTS OF MATALLIC ARSENIDES AND ANTIMONIDES, WITH CARBON MONOXIDE BEING OPTIONALLY INTRODUCED INTO THE REACTION AS A MODIFIER.

United States Patent Oflice 3,697,448 Patented Oct. 10, 1972 US. Cl. 252-464 2 Claims ABSTRACT OF THE DISCLOSURE A method and catalysts for selective hydrogenation and isomen'zation which involves contacting a feedstream with hydrogen and with various supported catalysts of metallic arsenides and antimonides, with carbon monoxide being optionally introduced into the reaction as a modifier.

This is a continuation-in-part of copending application Ser. No. 6,971, filed Jan. 29, 1970, now abandoned.

This invention pertains to selective hydrogenation.

In one of its more specific aspects, this invention pertains to the use of reduced nickel arsenate on alumina catalyst for the selective hydrogenation of diolefins to the corresponding monoolefins.

Various compounds of nickel are known as active and selective hydrogenation catalysts for conversion of diolefins to monoolefin. For extended use, compounds such as nickel sulfide require the continuous addition of small amounts of sulfur to maintain catalyst activity. Such addition can create a sulfur removal problem when the selectively hydrogenated products are to be further processed in other catalytic reactors in which minute amounts of sulfur are detrimental.

There has now been discovered a selective hydrogenation catalyst which does not require the presence of objectionable sulfur-containing auxiliary materials to maintain its selectivity. This catalyst can be employed to selectively hydrogenate diolefins to monoolefins, to double bond isomerize monoolefins in the presence of hydrogen and to hydrogenate reducible catalyst poisons such as sulfur, carbonyls, oxygen and acetylenes in the presence of monoolefins.

According to the method of this invention, there is provided a process for selectively hydrogenating unsaturated hydrocarbons to monoolefins, for isomerizing monoolefins in the presence of hydrogen and for hydrotreating olefinic streams containing minor amounts of materials such as compounds of sulfur, carbonyls, oxygen and acetylene which comprises contacting the stream comprising at least one of the aforementioned materials with hydrogen and with an after-described catalyst under reaction conditions.

According to this invention, the aforementioned contact is made with a catalyst comprised of a metal selected from the group consisting of iron, cobalt and nickel in the form of its arsenide or antimonide derivatives, or mixtures thereof.

Accordingly, it is an object of this invention to provide a simply prepared catalyst which possesses sustained activity.

It is another object of this invention to provide a selective hydrogenation process which is resistant to typical catalyst poisons and which can be used for sustained periods without requiring regeneration.

The method of this invention is broadly applicable to the selective hydrogenation of olefinic feedstocks. The

process is selective because it provides a method of hydrogenating materials such as acetylenic compounds, organic sulfur compounds, organic peroxides, carbonyl, compounds, cyclic and acyclic unsaturated hydrocarbons, and the like. However, the process is without substantial activity for the hydrogenation of monoolefins. In some instances, no hydrogenation of monoolefins is detectable.

When applied to a cyclic or acyclic unsaturated hydrocarbon, the process selectively hydrogenates these to cyclic or acyclic monoolefins with substantial selectivity depending upon the specific feeds, catalysts, and conditions used. Similarly, feedstreams which contain substantial amounts of monoolefins can be effectively hydrotreated to hydrogenate minor amounts of impurities, e.g., acetylenes, dienes, sulfur compounds, without significant conversion of the monoolefins to saturates. Thus, the invention is applicable for hydrogenating olefinic feedstocks where monoolefins are a substantial portion of the product. These product monoolefins can be present in the feed, or can be produced within the reaction zone as a hydrogenation product from a more unsaturated olefinic compound.

The olefinic feedstocks can be diluted with nonhydrogenatable or inert diluents. Olefinic refinery streams can be used as feedstocks.

Applicable unsaturated hydrocarbons are those olefinic hydrocarbons which have more than one double bond per molecule. For purposes of this invention, acetylenic hydrocarbons are also included in this scope, because both acetylenes and dienes, for example, can be selectively hydrogenated to monoolefins. In general, any unsaturated hydrocarbon, capable of being hydrogenated, can be selectively hydrogenated by the process of this invention. As a matter of practical commercial application, unsaturated hydrocarbons having up to about 15 carbon atoms per molecule are preferred. Some examples of these are acetylene, 1,3-pentadiene, 1,5-cyclooctadiene, 1,3,7-octatniene, 4 vinylcyclohexene, l,4,9 -decatriene, l,5,9'-cyclododecatriene, 2-hexyne, 3,4-dimethyl-1,6-tridecadiene, and the like and mixtures thereof.

Similarly, the monoolefins which can be subjected to the process of the present invention for hydrotreatment of impurities and/or double bond isomerization include any such cyclic or acyclic olefins which are normally hydrogenatable. As a practical matter, monoolefins of up to about 15 carbon atoms per molecule are of commercial importance and are preferred. Some examples of these are ethylene, propylene, butene-l, pentene-l, heptene-2, 4- methylpentene-l, 3-ethylcyclohexene, decene-S, octene-l, 4-ethyl-6-tridecene, and the like, and mixtures thereof.

As mentioned, the catalysts are the arsenide or antimonide forms of iron, cobalt and nickel. In its preferred form, the catalyst of this invention is a supported, reduced nickel arsenate. Such nickel-arsenic combinations as are satisfactory have the empirical formula NiAs in which x can have a value from about 0.33 to about 2.0, preferably 0.6 to 1.0, and include compounds such as NiAs, NiAs and Ni As the latter being particularly effective. However, the proportions of nickel and arsenic need not be stoichiometric; an excess of either the nickel or the arsenic can be present.

If the nickel is employed in its antimonide form, the combination will have the empirical formula NiSb in which x can have a value of from about 0.33 to about 2.0, preferably 0.6 to 1.0. Suitable forms are Ni'Sb, NiSb Ni Sb, Ni Sb Ni Sb Ni Sb and Ni Sb The proportions of nickel and antimony need not be stoichometric. Generally, the nickel is employed in the form of NiY in which Y is arsenic or antimony and x has a value from about 0.33 to about 2.0, preferably about 0.6 to about 1.0.

If cobalt and iron are substituted for nickel, the same empirical formula applies.

Generally then, the catalysts of this invention have the formula MY, in which M is a metal selected from the group consisting of nickel, cobalt and iron, Y is arsemc or antimony and x has a value from about 0.33 to about 2.0, preferably about 0.6 to about 1.0. Because of its greater selectivity, Y is preferably arsenic. i

For purposes of this disclosure, the invention w1ll be most frequently explained in terms of the nickel arsemde catalyst without meaning to limit the invention thereto. All uses and applications of any one of the catalysts specifically designated are intended to apply to all of the catalysts which are the subject of this invention.

While a supported type catalyst ispreferred, the catalyst can also be employed in a nonsupported state as, for example, in the form in which the principal components are coprecipitated from a sol.

In its supported state, any conventionally-employed nonacidic or relatively nonacidic catalyst support can be used. Preferable supports include gamma-alumina, alphaalumina, silica, charcoal, calcium aluminate, natural or synthetic molecular sieves and their combinations. In general, the granular support will have a surface area of about 1 to about 400 square meters per gram.

In the preparation of the catalysts, the nickel and arsenic, or antimony, can be simultaneously deposited on the support as; for example, by precipitating nickel arsenate or nickel antimonate on the support; or, the support can be impregnated with the nickel and the arsenic, or antimony, in individual treatments. In either instance, sufficient nickel is employed to deposit about 0.1 to about 20, preferably from about 0.5 to about 10, weight percent nickel on the support and sufiicient arsenic or antimony is employed so as to produce a finished catalyst containing from about 0.05 to about 50 weight percent, preferably 1.0 to ,10 weight percent, arsenic or antimony.

A suitable catalyst base can be conventionally impregnated with inorganic compounds, including acids, ammonium salts, nitrates, halides and so forth, of the metal concerned. For example, arsenic trioxide in an ammoniacal solution can be employed as an impregnant.

Under any method of preparation, the base, after deposition thereon of the materials concerned, can be washed to remove undesirable soluble salts, dried, calcined in air, and then reduced with hydrogen at any suitable temperature and pressure which is sufficient'to produce the active nickel arsenide or antimonide. For example, hy-

' drogen reduction at atmospheric pressure at 500 to 800 F. for 0. 1 to 20 hours can be used. In some instance, the calcination in airstep can be omitted.

The catalysts of the present invention have no appreciable skeletal isomerization ability; that is, when contacted with straight chain moonolefins or polyenes under the reaction conditions specified, they promote little branching of the molecule. Since the skeletal isomerization ability of a supported catalyst is generally a function of its acidity, which is largely contributed by the support, the use .of acidic supports which promote skeletal isomerization is to be avoided and nonacidic supports are preferred. This is due to the fact that such acidic supports do not give the selective hydrogenation results of the present invention. However, some mildly acidic supports, such as the flame-hydrolyzed alumiuas, are satisfactory for use in the present invention if their acidic character is minimized or destroyed during the catalyst preparation. Accordingly, ammoniacal solution or basic precipitants are preferentially employed in preparing the catalyst since the former act to reduce the acidity of the support, to avoid skeletal isomerization activity, and to provide a selective hydro genation catalyst.

The conditions under which the method of this invention is employed, whether for selective hydrogenation or poison removal by hydrogenation, can vary widely. Generally, the reactions are conducted by passing thehydrocarbon stream, as avapor, with hydrogen, into contact with catalys he reaction zone being maintained at a temperature of from about 75 F. to about 750 F., preferably from about 200 F. to about 600 F., at a pressure of from about atmospheric to about 1000 p.s.i.g. The hydrocarbon stream is passed in contact with the catalystat a rate sufficient to provide a liquid hourly space veloc ty (LHSV) of from about 0.1 to about 10. Hydrogen is 1ntroduced at a rate which provides a hydrogen to feed molar ratio of from about 0.1 to 1 to about 5 to 1.

The selectivity of the process and catalyst of this invention can be improved by incorporating carbon monoxide in the feedstock. Carbon monoxide in amounts from about 500 to about 5000 ppm. of the feedstream have been found to be eifetcive. The carbon monoxide can be introduced with the feedstock, with the hydrogen, or it can be separately introduced.

The catalysts of this invention can be regenerated in a number of ways including conventional calcination in diluted air. Inasmuch as the reaction conditions-to which these catalysts are subjected are relatively mild, catalyst regeneration can be primarily directed to the removal of viscous oil deposits. Accordingly, the catalysts can be regenerated by removing these deposits by oxidation or by washing with a liquid aromatic solvent under conditions suitable for removing the deposits. Preferably, benzene, toluene, xylene, and mixtures thereof are passed through the catalyst bed at a temperature such as 200'- 250 F., the bed being thereafter flushed with warm hydrogen or an inert gas.

The catalysts of the present invention, particularly in the nickel arsenide form, Ni As are suitable under the reaction conditions previously set forth, for the double bond isomerization of monoolefins. Best results are obtained at 350600 F., preferably at 400500 F. In this application, nonacidic supports are employed. An amount of hydrogen sufiicient to keep the catalyst unimpaired, or clean, is employed. Carbon monoxide can also be included in the feed.

The following examples indicate methods of preparing the catalysts of this invention and their employment in the method of this invention.

EXAMPLE I A nickel arsenide catalyst was prepared by impregnating a catalytic grade alumina gel base with sulficient nickel sulfate to provide 4.25 weight percent nickel based on the weight of the alumina. The nickel-impregnated alumina was then impregnated with a stoichiometric amount of sodium arsenate. The impregnated base was then washed to remove soluble salts, dried and reduced with hydrogen at atmospheric pressure and at a temperature of about 520 to 600 F. for one and one-half hours to form the Ni As -containing catalyst.

EXAMPLE II A nickel arsenide catalyst was prepared as follows 98.5 grams of nickel nitrate, Ni(N0 -6H O, were dissolved in 1200 ml. of distilled water and 150 g. of finely divided, flame-hydrolyzed alumina were added to the solution to produce a slurry. To this slurry, 32.1 grams of arsenic acid, H AsO dissolved in 300 ml. of distilled water were added. The resulting slurry was neutralized with ammonium hydroxide to a pH of 7.

The mixture was filtered and the solids were washed with distilled water, refiltered, dried, and heated to 1000 F. at which temperature they were maintained for two hours. The solids were then ground and screened and grams of a 9 to 20 mesh catalyst were recovered. This catalyst contained 9.8 percent nickel, 9.1 percent arsenic, had a surface area of 70 mi /gm. and a pore volume of 0.63 cc./gm. Before use, the catalyst is reduced in the presence of hydrogen at 520 to 600 F.

EXAMPLE III A charcoal-based catalyst was prepared by impregnatmg 6/ 14 mesh cocoanut charcoal with a nickel acetate solution. The impregnated charcoal was dried at 250 F. and impregnated with H As dried at 250 F. and washed with aqueous ammonia. Activation was accomplished by heating at 800 F. in hydrogen for two hours, the air calcination step being omitted. The catalyst is active for selective hydrogenation of unsaturated hydrocarbons.

EXAMPLE IV Due to the low solubility of most antimony compounds, different techniques were used to make the antimonycontaining catalysts. One suitable method was to dissolve antimony trioxide (Sb O in a water solution of tartaric acid containing a small amount of nitric acid. This step formed an antimonyl tartrate compound. The required amount of nickel acetate or nickel nitrate was then dissolved in the tartrate solution to form a clear green solution containing both nickel and antimony. This solution was then used to impregnate the preformed catalyst base pellets, which were dried, and then calcined in air at 900 to 1000 F. to remove the organic portion of the impregnating compound. The calcined catalyst was then heated in a stream of hydrogen at 500 to 900 F. after which it was ready to use.

Similar methods to the above have been employed to support both nickel-arsenide and nickel-antimonide on silica, Celite, and calcium aluminate (CaAl O' supports, the resulting catalysts in all instances being effective for selective hydrogenation.

EXAMPLE V The catalyst prepared in Example I was employed for the selective hydrogenation of a stream comprised of substantial amounts of 4-vinylcyclohexene in cyclohexane diluent. The conditions under which the run was conducted, and the selective hydrogenation effected, are

indicated by the following:

Product from selective hydrogeuating with NlaASa on alumina These date indicate that the catalyst and method of this invention are effective in selectively hydrogenating 4-v1- nylcyclohexene to primarily monoolefinic compounds.

EXAMPLE VI The following illustrate the effectiveness of the method and catalyst of this invention in hydrotreating a stream of mixed monoolefins. This mixture of polymerized lower olefins (cat poly-gasoline) was used as a feedstock to an olefin disproportionation reaction to produce isoamylenes for isoprene manufacture. This stream was hydrogenated for the purpose of reducing the concentrations of certain undesirable materials such as sulfur compounds and carbonyl compounds such as aldehydes and ketones. Operating conditions and results are presented when employing a nickel arsenide catalyst similar to that prepared in Example I.

Operating conditions:

Temperature, F.475 Hydrogen pressure, p.s.i.g .100 Liquid hourly space velocity-2.7

Feed Product Stream Carbonyls, p.p.m 115 2 Sulfur, p p m 7 5 Saturates weight percent 3.3 3.7 Maleic anhydride value 5. 2 4. 6

The above data illustrate that the method and catalyst of this invention reduced the sulfur, conjugated diene and carbonyl concentration of the highly olefinic feedstream without significant increase in saturates.

EXAMPLE VII Operating conditions:

Temperature, F.5l0 Hydrogen pressure, p.s.i.g. Liquid hourly space veloeity2.5

Stream Feed Product Sulfur, p n m 253 95 Maleic anhydride value 28. 7 6. 0 Saturates, weight, percent--- 28. 2 29. 3

These data indicate a significant reduction in sulfur content and in diolefin content. The increase in saturate content is nonsignificant since the values are within the accuracy of the test method employed.

EXAMPLE VIII The method and catalyst of this invention are effective for selective hydrogenation of 1,5-cyclooctadiene to cyclooctene as shown by the following series of runs in which cyclooctadiene was passed with hydrogen over a catalyst comprising 8.6 weight percent nickel and 8.6 weight percent arsenic on an alumina base.

The catalyst was comprised of 25 percent Ni As on alumina, the catalyst being 10/20 mesh and having a surface area of 83 mfi/g. and a pore volume of 0.73 ml./ g. In all instances, carbon monoxide was introduced into the reaction and had the effect, as previously mentioned, of modifying the extent to which the selective hydrogenation took place.

Run Number I II III IV V VI Catalyst quantity, gms. 13. 9 13. 9 13. 9 13. 9 13.9 13. 9 Reaction pressure,

p.s.i.g 115 215 215 315 315 Reaction temperature,

0. 954 0. 448 1. 10 0. 563 1. 050 1. 080 0. 046 0.022 0.053 0.027 0. 052 0. 053 Cyclohexane 0. 599 0. 602 0. 569 0.255 0. 251 0. 602 Lil-cyclooctadiene..- 0. 052 0. 053 0. 049 0. 018 0. 022 0 052 0; product distribution, percent:

Cyclooctane 1. 25 1. 09 2. 39 7. 10 8. 64 2. 94 Cyclooctene 97. 60 97. 68 97. 60 92. 89 91. 36 97. 06 1,3-cyclooctadiene. 1. 13 1. 19 0.01 0.01 01 01 1,4-cyelooctadiene 0. 07 0. 03 01 01 01 01 1,5-eyclooetadiene- 0. 06 0. 01 01 01 01 01 These data illustrate that the invention catalyst inhibited with carbon monoxide shows excellent selectivity and that it is possible to reduce diolefin content to less than 0.05 percent and maintain excellent selectivity to cycleoctene. Under these conditions in the absence of CO, complete conversion of cyclooctadiene to cyclooctane can occur.

The selective hydrogenation of cyclooctadiene, as shown above, has been elfectively carried out in runs of up 80 hours in duration. This demonstrates the highly desirable long-lived characteristic of this catalyst system and process.

The eifect of the addition of carbon monoxide is also shown in the employment of the method and catalyst of this invention for the selective hydrogenation of acetylene.

EXAMPLE IX The following runs, in which streams containing acetylene and ethylene were hydrogenatedv with, and with- 8 EXAMPLE X Reactor M 1 Moles per hour Product distribution, weight percent cyclo'octa- Cyclooctadiene Run diene gar Hydro- Oyclo- Cyclo- No. F. p.s.i.p. mole of 0 Hydrogen carbon 1,5 1,4 1,3 oetene octane out, the presence of carbon monoxide, were conducted employing a nickel arsenide agent, on alumina, the quantities of nickel and arsenic being 8.3 and 7.6 weight percentof the total catalyst, respectively. The runs were made under comparable conditions, the carbon monox-- ide being introduced into the reactor as a gas with the The results indicate that the addition of carbon monoxide improves the selectivity of the method and the catalyst for the hydrogenation of acetylene in preference to ethylene. In the absence of 00, more ethylene was destroyed as evidenced by the analysis and the temperature use.

In other runs the use of carbon monoxide has been found to produce similar results with the other catalysts of this invention. This has been particularly true of nickel arsenide on alumina for selectively hydrogenating acetylene in ethylene during operating periods of up to 600 hours.

The introduction of carbon monoxide into the reaction zone is also effective in improving the selectivity when hydrogenating diolefins to monoolefins in respect to minimizing the extent of monoolefin hydrogenation. This is illustrated by the following example involving the selective hydrogenation of 1,5-c'yclooctadiene to cyclooctene at various levels of carbon monoxide concentration in the reaction zone.

These data show that carbon monoxide prevents runaway conversion to cyclooctane and illustrate an increasing selectivity in the conversion of the cyclooctadiene by cyclooctene with an increase in carbon monoxide to 1,5- cyclooctadiene ratio. This is particularly evident at higher reactor pressures as shown by comparison of Run 3 with Run 4.

The selective hydrogenation of cycloocetadiene has been carried out with the various catalysts of this invention in runs of up to '80 hours in duration.

As mentioned, the method and catalysts of this invention are also suitable for the double bond isomerization of monoolefins. The following is illustrative of this.

EXAMRLE XI A catalyst comprising Ni As on alumina, prepared in accordance with one of the previously described methods, was contacted with a mixture comprising 10 percent pentene-l and percent cyclohexane at the rate of 3.1 volumes of feed per hour per volume of catalyst. Hydrogen and carbon monoxide were introduced into the reaction zone, as a mixture containing 2 percent carbon monoxide in hydrogen, at a rate of 600 volumes of the mixture per hour per volume of feed. Initial reaction conditions were 375 F. and p.s.i.g. Under these conditions, 15 percent of the pentene-1 was converted to cisand transpentene-Z-isomers.

The reaction conditions were then altered to 475 F. and 200 p.s.i.g., under which conditions an equilibrium mixture of double bond isomers of pentene was produced,

at which point the reaction mixture was comprised of about one part pentene-l, about. three parts cis-pentene-2 and about six parts trans-pentene-Z. Only 2 percent of the of the original pentene had been hydrogenated to pentane.

In the double bond isomerization of monoolefins as described above, the presence of carbon monoxide has also been found effective in limiting the extent to which hydrogenation takes place. Further, because of its relative insensitivity to typical catalyst poisons, such a process is capable of long operating periods between regenerations.

One acceptable procedure for regenerating the catalyst by solvent washing is described in the following.

EXAMPLE XHI A bed of contaminated nickel arsenide on alumina catalyst which had become spent in the selective hydrogenation of acetylenes in ethylene in accordance with the method of this invention, was washed with toluene and a viscous residue amount to about 18 percent of the catalyst was washed from it. The catalyst was then blown substantially dry with warm flue gas and returned to service. A comparison of its activity, after regeneration, with the activity of a nonregenerated portion of the spent catalyst was as follows:

1 Uncontrollable temperature increase due to runway conversion of ethylene to ethane. Estimated 50% conversion of ethylene to ethane. These data indicate the effectiveness of the extraction method of catalyst regeneration employable with the method and catalyst of this invention in restoring the selective hydrogenation ability of the catalyst.

EXAMPLE XHI Cyclododecatriene was selectively hydrogenated to cyclododecene over a relatively low surface area aluminasupported nickel arsenide catalyst. The catalyst contained 9.0 weight percent nickel, 9.7 weight percent arsenic and had a surface area of 14.8 mF/g. A weight percent mixture of cyclododecatriene in c'yclohexane diluent was hydrogenated during passage through a fixed bed of this catalyst. The temperature was 410 F., the pressure was 100 p.s.i.g., and the feed rates for the cyclododecatriene, hydrogen, and carbon monoxide were 8.09 10- 3.61 X 10-, and 7.4 10- moles per hour-gram of catalyst, respectively. The results of the run are shown by the analysis of the C compounds in the efiluent:

C product: Weight percent These data illustrate that the cyclododecatriene was completely converted. Also, they indicate that the cyclic triene was very selectively converted to the cyclic monoolefin with little complete hydrogenation of the cyclic triene to the saturated compound and with only a minor amount of bicyclic formation.

It has been found that ferric and ferrous arsenides are particularly effective in converting acetylenes to monoolefins or to polymers in the presence of diolefins with substantially no conversion of the diolefins themselves. Similarly, ferric and ferrous arsenides are effective in converting acetylenes to monoolefins in the presence of diolefins and monoolefins without substantial conversion of either the diolefin or monoolefin.

Both the ferric arsenide and the ferrous arsenide catalyst can be prepared in a number of ways which embody the same general principles embodied in the preparation of the nickel catalyst. That is, the iron and arsenic, or antimony, can be simultaneously deposited on the support by precipitation or the support can be impregnated with the iron and arsenic or antimony from suitable solutions. In any instance, the ferric or ferrous iron is employed to deposit about 0.1 to about 20, preferably from about 0.5 to about 10, weight percent iron on the support and sufiicient arsenic or antimony is employed so as to produce a finished catalyst containing from about 0.05 to about 50 weight percent, preferably 1.0 to 10 weight percent, arsenic or antimony.

The following methods of preparation are illustrative of but two or these.

In the preparation of ferric arsenide catalysts, 104 g. of a pilled commercial gamma-alumina catalyst were immersed in an aqueous solution of ferric nitrate and arsenic acid, prepared by dissolving 15 g. of Fe(NO -9H O and 6 g. of H AsO in 150 ml. of deionized Water. After 2 hours of contact, the pills were then calcined in air at 1000 F. for 4 hours after which they were contacted with hydrogen at 800 F. for 4 hours to reduce the ferric arsenate to ferric arsenide.

In the preparation of the ferrous arsenide catalyst, 6 g. of H AsO were dissolved in ml. of water. Seventeen and six-tenths grams (17.6 g.) of FeSO' -7H O were dissolved in 150 ml. of water. The two solutions were combined and 50 g. of Alon-'C alumina were mixed with the solution. Ammonia was added to the mixture until the mixture had a pH of 8. At this pH, ferrous arsenate precipitated out and the precipitated ferrous arsenate and Alon-C alumina were separated from the liquid and dried. The solids were then calcined in air at 1000 F. for one hour after which they were contacted with hydrogen at 800 F. for about 16 hours to reduce the ferrous arsenate to ferrous arsenide.

Conversions employing the aforementioned iron catalysts were conducted using a refinery-produced butadiene concentrate with both catalysts. The C fraction of this concentrate had the following composition by gas liquid chromatography:

Component: Mole percent, 0., basis n-Butane 34.65 l-butene and isobutene 12.56 t-Z-butene 3.54 c-Z-butene 2.83 LEI-butadiene 45.62 1,2-butadiene 0. 17 l-butyne 0.08 Vinylacetylene 0.54 2-butyne 0.01

In the employment of the ferric arsenide catalyst, according to the method of this invention, the reaction was conducted at 250 F. and 500 p.s.i.g. at a butadiene concentrate WHSV of 0.6 and a hydrogen GHSV of 560. Analysis of the product was as follows:

These data indicate that all of the C acetylenes and all of the 1,2-butadiene had been hydrogenated with no loss of 1,3-butadiene.

In the employment of the ferrous arsenide catalyst according to the method of this invention, the reaction was conducted at 315 F. and 600 p.s.i.g. at a butadiene con- 1 1 centrate WHSV of 2.0 and a hydrogen GHSV of 500. Analysis of the product was as follows:

These data indicate that all of the vinylacetylene had been hydrogenated with a 12 percent loss of 1,3-butadiene by hydrogenation.

It will be noted that the method of this invention employing the iron-containing catalysts can be carried out at somewhat lower temperatures than those temperatures previously defined for the nickel catalysts converting diolefins to monomers, that, is, at temperatures from about 200 to about 400 F.

The aforementioned butadiene concentrate was contacted with a nickel a-rsenide catalyst and hydrogen for the purpose of carrying out those conversions conducted with the ferric and ferrous arsenides. This nickel arsenide catalyst had been prepared by dissolving 98.5 g.

in 12.00ml. of water to which were added 150 g. Alon-C alumina to make a slurry. To the slurry were added 32.1 g. H3ASO4 in 300 m1. H O giving a slurry of pH 1.6. Ame monium hydroxide was added until pH 7 when precipitated. The slurry was then filtered, washed with waterand filtered again. The slurry was then heated 16 hours at 212 F.; the catalyst was calcined at 1000 F. for 30 minutes after which it was cooled, ground and sieved to .10/ 20 mesh. The catalyst had an arsenic content of 8.6

weight percent, a surface area of 83 mF/g. and a pore volume of 0.73 mL/g.

In a first run conducted at 200 p.s.i.g., 218 F., a butadiene concentrate feed rate of 1.4 WHSV and a hydrogen feed rate of about 600 GHSV, all of the acetylenes and all but a trace of 1,2-butadiene were hydrogenated. However, about 12 percent of the 1,3-butadiene was also hydrogenated.

It will be evident from the foregoing that various modifications can be made to the method of this invention. However, such are considered as being within the scope of the invention.

What is claimed is:

1. A catalyst for the selective double bond isomerization of monoolefins consisting essentially of nickel arsenide of the formula NiAs on alumina wherein the amount of nickel present is in the range of about 0.1 to about 20 weight percent and x is in the range of about 0.6 to about 1.0.

2. A catalyst according to claim 1 wherein the nickel arsenide is Ni As and the amount of nickel present is in the range of about 0.5 to about 10 weight percent.

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252-455 Z, 456, 466 J; 260-677 H, 683.2 

